Vehicles can encounter many situations in which they should alert persons, vehicles, and the like, of their presence in order to avert a potential collision or otherwise prevent the vehicle coming within an unsafe distance of an external object. As one example, a pedestrian who crosses the road in front of the vehicle can be jaywalking or may not be paying attention to the approach of the vehicle. The driver of the vehicle can use the vehicle's horn to alert the pedestrian. However, a horn will typically have an acoustic radiation pattern that is sub-optimal in that it may not be sufficient to warn the pedestrian that the horn being honked is intended for him/her. Instead, other pedestrians or other drivers in the vicinity of the vehicle can believe the horn is being honked at them. Moreover, a pattern of the sound waves emitted by the horn can make it difficult to localize the source of the horn. From the perspective of the pedestrian, the horn can be perceived as coming from another vehicle. Furthermore, the horn can cause the pedestrian to look in a direction other than the direction of the vehicle that generated the horn honk, thereby potentially distracting the pedestrian from the actual source of the horn.
Additionally, electric vehicles can be difficult to audibly detect due to low levels of emitted noise from an electric and/or hybrid propulsion system (e.g., lack of combustion engine noise and/or lower levels of tire noise) making it difficult for others to hear the vehicle as it travels. Further, the reaction time required for a vehicle to generate an alert, and the reaction time of a person (or other vehicle) after hearing the alert, are such that relying solely on outputting an alert to avert a potential collision or an approach of the vehicle within an unsafe distance of an external object is inadequate, especially for many close-encounter collision scenarios.